Do the exhaust first. You need it for any cam upgrade. I have EMI with long risers with no silent choice. Do not get short risers if you plan on doing a cam upgrade. Exhaust will give you about 1 or 2 MPH on a stock engine. Good Luck!!

Yeah to what he said! The Merc 454/365hp engine comes stock with all the good forged internals,......but the FIRST thing you need is a better breathing, aftermarket exhaust system such as a Stainless Marine, GIL, Dana or something comparable to those. An upgraded exhaust is the only way you are to make more TRUE HP in a naturally aspirated engine with other internal upgrades like a cam, head porting, intake manifolds, carbs, etc. If you really want it to RUN, then you gotta let'er breath out the exhaust FIRST before she will buck for you

If you simply bolt a blower on your 365, then you would not neccessarily need an upgraded exhaust system, however anytime you can add a better breathing exhaust system over the Merc stock exhaust is a HUGE improvement!

By the way, you do not need to change the heads on those 365's....just have them checked for cracks between the seats, then have them bowl/pocket ported while paying attention to the short side radius. "JimV" (Michigan) would be good for that 616-889-0928. Add a Holley 750cfm carb, single plane intake, roller rocker arms, then for a cam selection you can install a good hydraulic roller and HANG ON! For the custom cam I recommend "RMBuilder"/Bob Madara of Marine Kinetics in N.Y. 585-654-8583---he's the cam guru and will grind you a cam profile for your combination and specific application. Have fun.

man, i love this forum.

would the emi manifolds in the classifieds be a good set or are they basically just replacements for oem?

Scratch that last question... guess if I would have read the whole add the first time I would have seen they're not for use on engines with performance cams.